Evaluating Alternative Operations Strategies to Improve Travel Time ...

SHRP 2 L11: Final Report
deal with unreliability. It is desirable if agencies focus on reporting and evaluating the Planning-
Time Index since this measure is better understood by engineers.
Travel-time reliability performance measures also play a key role in evaluating the effectiveness of
ITS strategies used to provide traveler information and reduce congestion. In a funding-restricted
environment, it is important that agencies wisely invest their scarce resources on ITS technologies
that will improve the system performance and capacity at a minimum cost. With the performance
measure indexes, and effective tools to forecast them, agencies will be able to quantify the impact
of the deployed ITS technologies and, therefore, prioritize investments in the future.
Appendices B and C present an approach to determining the economic value of
improving travel-time reliability. In this approach, uncertainty is converted to a
certainty-equivalent measure in order to use conventional evaluation methods to
place a value on the cost of unreliability. The certainty-equivalent measure is a
method that allows us to express the value of reliability in terms of the increase in
the average travel time a person would accept to eliminate uncertainty. The value
of reliability can be derived for multiple user groups or market segments by
applying a separate value of time that corresponds to each user group along with
the observed average volume for each user group on the roadway segment. The
total value of reliability is then computed as the sum of the reliability values for
each user group on the highway segment. The concept for calculating the value of
travel-time reliability is illustrated in Figure 7.1.
Figure 7.1Appendix D provides an example of this methodology based on actual data from Seattle,
Washington. This example determines the economic benefits of improving travel-time reliability
through the implementation of ramp meters under recurring congestion. In this example, the
uncertainty arising from recurring congestion is converted to a certainty-equivalent measure in
order to use conventional evaluation methods to place a value on the cost of unreliability.
Existing Stakeholder Roles and Responsibilities
The following is an overview of the various stakeholders and what they are currently doing to
improve travel-time reliability.
USDOT
• Reliability policies have been established to promote the importance of reliability as a
key performance measure and promote its implementation by agencies.
• Limited performance-measures data are being collected.
• Funding for reliability research and improvements has been provided.
State DOTs
• Very limited congestion-based facility tolling has been implemented.
• Ramp-metering is much more common than tolling and congestion pricing; bottleneck
elimination also contributes to boosting reliability.
• Some performance-measures data are available for some of the state roadways, but
there is limited reporting of this data.
• Some truck lanes at ports of entry and weigh-station bypass lanes are provided.
• Traveler information is provided using various delivery methods.
A CONCEPT OF OPERATIONS Page 101